The invention relates to a device for adjusting the phase angle between two rotating, drive-connected elements with an adjustment device arranged between the two rotating elements.
Devices of this type are known, for example, in internal combustion engines and are provided there for the relative adjustment of the phase angle of the camshaft and a crankshaft which drives the camshaft. This engagement in the valve drive kinematics influences the phase angle of the valve opening, the opening period and the valve stroke in a variable fashion within limits.
Known hydraulic camshaft actuators for adjusting a phase angle of a camshaft, which activates the valves of an internal combustion engine, comprise essentially a hydraulic motor which is fed by the motor oil circuit, operating for example according to the vane cell principle. Electric camshaft actuators composed of a summing gear mechanism and rotational actuator have recently become known in which an electric motor or an electric brake serves as the rotational actuator. All the systems have to place the phase angle of the camshaft in a defined emergency running position if faults occur in the electronics, that is if electric cables, or sensor systems or the actuator systems fail, or if the electric motor, the brake and the like become inoperative to ensure that the internal combustion engine remains operative although with restrictions. In hydraulic camshaft actuators with their typically small actuating ranges, this emergency running position is generally located at an end stop of the camshaft actuator. As a result of the average camshaft torque, these camshaft actuators generally move without an oil supply to the late stop, which may be, for example, the emergency operating position for an inlet valve of the internal combustion engine. If the “early” stop is the emergency operating position which is to be set, a restoring spring usually disposed between the chain wheel and camshaft comes into use. To avoid noise, the camshaft actuator is generally locked in the emergency running position.
In order to ensure the operation of internal combustion engines with camshaft actuators with an extended actuating range in the event of an emergency, an emergency operating position between the stops should expediently be provided. This may be done, for example, by means of two rotational springs, one operating counter to the other, between the chain wheel and camshaft whose effect is canceled out in the emergency operating position. However, during normal operation the camshaft actuator must operate continuously counter to these springs with the result that its power drain in terms of pressurized motor oil or electric current is in some cases considerably increased.
German laid-open patent application DE 102 20 687 discloses a device for adjusting the angle between two rotating, drive-connected elements in which, in the event of a failure of the adjustment device and/or its controller, an emergency position can be reached and held by braking and locking the adjustment shaft and by rotating the drive shaft with a suitable transmission ratio.
It is the principle object of the invention to provide a low power consumption device for adjusting the angle between two rotating, drive-connected elements which permits an emergency running position to be reliably adopted and held.